This invention relates to a hot-melt adhesive based on vinyl polymer and to a process for adhering surfaces therewith.
Hot-melt adhesives are bonding agents which achieve a solid state and resultant strength by cooling, as contrasted with other adhesives which set or harden by chemical reaction or loss of solvent or water vehicle. Prior to heating the hot-melt adhesive is a thermoplastic material in the form of a 100% by weight solid. Application of heat melts the adhesive so that it can be readily applied to the substrate desired. After removal of heat, the adhesive returns to the solid state by simple cooling.
Combinations of polymers and copolymers containing polyethylene, rubbers and the like have been proposed in the past as the basic component of hot-melt adhesive compositions. Often such compositions include several ingredients additional to the base polymer to improve specific properties of the adhesive such as its viscosity in the molten state (melt viscosity), peel strength, flexibility, stability and the like.
The base polymer currently of choice for use in hot-melt adhesives designed to give good adhesion between polar and nonpolar surfaces is a copolymer of ethylene and vinyl acetate. Such polymers are produced by polymerizing ethylene and vinyl acetate at very high pressures of 15,000 to 40,000 psi (1055-2812 kg/cm.sup.2) and at temperatures of from 150.degree. to 250.degree. C. A hydrocarbon wax is generally added to the copolymer thus obtained in amounts of 25 to 50% by weight of the total mixture to improve the hot-melt performance of the copolymer. Such waxes as are employed, however, have become increasingly costly and difficult to obtain due to the uncertainty in supply of petroleum available.
It is an object of the present invention to provide a novel hot-melt adhesive based on a polymer derived from higher alpha-olefins which requires no hydrocarbon wax yet performs comparably to commercially available hot-melt formulations.
It is another object to provide a process for adhering surfaces with such an adhesive.